Security documents have a substrate, which may be flexible, and on or in which there is arranged at least one security feature for the verification of the authenticity of the security document.
Volume or surface holograms or refractive gratings have, inter alia, been suggested as security features, in particular for bank notes, credit cards or passports. Even though such features are hard to counterfeit, they can be imitated if sufficient efforts are undertaken by a counterfeiter.